Genetic and biochemical analyses of tRNA precursors synthesized by the bacteriophage T4 have suggested that both the quality and quantity of mature product is regulated at the level of processing. In microbial systems, tRNAs generally arise from di- or multimeric precursors which are matured by a number of enzymes; the best studied of these is RNase P, an endonuclease which generates the mature 5' tRNA termini. Determination of the primary sequences of a number of RNase P substrates has allowed us to conclude the clear absence of sequence-specific enzymatic recognition. Two factors which do appear to be crucial for proper enzyme-substrate interaction are the conformation of the precursor and the state of maturation of its 3' terminus. Experiments currently in progress and planned for the next year are designed to test our hypothesis that the accurate and efficient recognition of tRNA precursors by their processing enzymes depends upon many of the same structural properties which are required for their ultimate function.